During operation, electronic devices typically generate heat. Often, this heat is not only unwanted, but may lead to premature failure of the electronic device. Many electronic devices utilize heat sinks, fans (or a combination of the two) or other cooling systems in order to cool the device and reduce the possibility of a premature failure. Unfortunately for many electronic devices, the cooling system, or fan, itself is one of the components that is most prone to failure because it involves a moving device that utilizes, for example, bearings that sometimes freeze in place or fan blades that may collect so much dust that they can no longer turn. Furthermore, even when the cooling system is electrically and mechanically operational, other issues may prevent cooling effectiveness, including blockage of air passages. An example of such an electronic device is a personal computer. The personal computer has several components that produce so much heat that, without active cooling, the temperatures of these components would reach a point where either the device fails, or an internal mechanism shuts down the device until the temperature falls into a suitable operational range for the component.
In many applications, the electronic device is at least partially enclosed in a cabinet, chassis, case, or the like. As the electronic device operates, heat is produced by the components of the device and the temperature of the air within the enclosure also increases as a result of the heat generated by the components. With current technology, when the temperature reaches a certain point, actions are taken to actively cool the system. These actions may include activating a fan located near the heat producing component(s) to produce air movement over the component or activating a fan that will force an exchange of air between the outside of the enclosure and the inside of the enclosure. Since the air outside the enclosure is generally cooler than the air inside the enclosure, the net result should be a reduction in the temperature of the air within the enclosure. Unfortunately, as noted above, these fans sometimes fail. The failure of a fan may or may not cause the system to reach a temperature where it automatically shuts down. If the fan failure does cause the system to shut down, the user may be faced with a random failure and a potential loss of data, such as data entered subsequent to the most recent “save” command. If it does not cause the system to shut down, the internal temperature may still cause secondary failures of components. For example, if the system has a hard disk drive, which typically does not generate a significant amount of heat, continued operation of the hard disk drive at high temperatures may cause an early end-of-life for the disk drive motor or the electronics associated with the disk drive.
Thus, there is a need to detect if, after the fan speed has been increased, the fan is actually performing its intended cooling function. A tachometer may have been employed to determine if the fan was operating, but is really only an accurate way to tell if the shaft of the fan is turning, but not if the blades of the fan are turning. However, if the fan blades are slipping on the fan shaft, then the fan isn't effectively moving air, even though the shaft is turning and the tachometer may indicate that the fan is operating properly. Additionally, the tachometer and the associated circuitry used to measure fan shaft speed add cost to the electronic device. Therefore, a system for making sure the fan is actually having the desired cooling effect, and notifying the user when it isn't having the desired cooling effect, is needed.